White bread may bring greater disease risk

Foods with a high glycemic index (GI), such as most white breads, lead to a higher risk of certain health problems, according to researchers at the University of Sydney, Australia.

The study found that high blood glucose led to a higher risk of type 2 diabetes and heart disease, and was also linked to gall stones and some types of cancer, providing further evidence that could trigger greater demand low GI and multi grain foods.

The researchers concluded: "Low-GI and/or low glycemic load (GL) diets are independently associated with a reduced risk of certain chronic diseases. In diabetes and heart disease, the protection is comparable with that seen for whole grain and high fibre intakes. The findings support the hypothesis that higher postprandial glycemia is a universal mechanism for disease progression."

High grain breads, and other low GI foods, are therefore recommended in the promotion of a healthier diet.

Between 2003 and 2006, the number of new whole grain product launches fairly doubled every year - from 64 in 2003, to 140 in 2004, to 346 in 2005, to 620 in 2006, according to Mintel.

This reflects the race by food manufacturers to carve out a slice of the market during the initial period of rapid growth, which ran parallel to the growth in consumer awareness of the healthy grains.

The researchers had found that results from previous observational studies had been inconsistent and had prolonged the controversy over the effects of GI and GL on the risk of certain chronic diseases.

In their study the researchers employed meta-analysis techniques, that incorporated the results of 37 studies. The studies were further stratified according to the validity of the tools used to assess dietary intake.

A statement from the University of Sydney drew attention to the fact that the diets of nearly two million healthy men and women worldwide were reviewed.

The researchers confirmed that for the comparison between the highest and the lowest quantiles of GI and GL, "significant positive associations were found in fully adjusted models of validated studies" for all the diseases combined."

The University statement quotes lead author Alan Barclay as saying: "If you have a constantly high blood glucose and insulin levels due to a high GI diet, you may literally 'wear out' your pancreas over time. Eventually it may lead to type 2 diabetes in older age."

However, he said that he was more surprised by the relationship between GI and some of the other diseases. With regard to cancer he concluded: "This is because constant spikes in blood glucose that cause the body to release more insulin also increase a related substance called 'insulin like growth factor one' (IGF-1). Both these hormones increase cell growth and decrease cell death, and have been shown to increase the risk of developing cancer."

The University statement defines high GI foods as carbohydrates that break down quickly during digestion, causing blood glucose levels to increase quickly and stay higher for longer, for example most biscuits.

Low GI carbohydrates break down more slowly during digestion, releasing glucose gradually into the bloodstream, with leading examples including muesli, whole- or multi-grain bread and fruit.